My apologies in advance if this has already been answered, but every search I have done does not come close to what I need. Also, this is all pseudo code.
Here is the situation: I created a form (targeting DOT NET 3.5) that does a loop on a gridview recreating a class and runs the code. After the code runs, there is a local variable on the class that gets updated and allows me to use it and the process repeats. Something like this:
For x as Integer = 0 to Me.txtTextBox.Lines.Count - 1 'Can be in the hundreds
Dim objMyClass as MyClass = New MyClass(Me.DatagridView1.Rows(x).Cells(0).Value)
if objMyClass.Start() = True then
'Do my thing with objMyClass.LocalLongVariable
End If
Next
This works just fine, but takes literally days to complete. The last time I ran this it took like 6 days, 7 hours and 40 something minutes to complete and barely bumped the CPU usage.
So, now I want to use MulitThreading to run several of these instances at the same time. I have not been able to get this to work. Everything I try returns different values every time I run it (and it should not). I believe that the threads are accessing the local variable across other threads and are incrementing at will. And SyncLock locks up the entire program. I have also tried adding a custom event that fires when the process is completed and executes a delegate on the Main form, but that has not worked either.
Now, my question is simple: How can I run multiple threads using the same base class (passing a unique string variable) and have the local class variable produce the correct results back to the UI? (And, from what I have been reading, the BackgroundWorker class in not suitable for this many threads (like hundreds); correct me if I read it incorrectly please)
I am looking for something like:
Dim thrd(Me.txtTextBox.Lines.Count) as Thread
Dim objMyClass(Me.txtTextBox.Lines.Count) as MyClass
For x as Integer = 0 to Me.txtTextBox.Lines.Count - 1
thrd(x) = new Thread (Sub()
objMyClass(x) = New MyClass(Me.GridView1.Rows(x).Cells(0).Value
If objMyClass.Start() = True Then
'Do my stuff here (maybe call a delegate??)
End If
End)
thrd(x).IsBackground = True
thrd(x).Start()
Next
Any help/advice on how to proceed will be greatly appreciated. And, if you know of any examples of your suggestion, please post the code/link.
The solution was, in fact, Synclock. My issue was that I was locking the wrong object, objMyClass, instead of the current Me AND I was failing to use Monitor.PulseAll(). Also, I switched to using the ThreadPool.QueueUserWorkItem(AddressOf objMyClass, args) and also used SyncLock on my custom event raised when the thread completes. It's a whole lot easier!! Thanks!!
Related
I am working on a VB.NET Windows Forms application where the user is supposed to be able to determine how many processes the application is allowed to launch at a time.
My current method mostly works but I've noticed that occasionally the application goes over the set amount. I use two global variables for this, _ConcurrentRuns which is 0 at the start of the application, and _MaxConcurrentRuns which is set by the user.
Private _sync As new Object()
' This is called Synchronously
Private Function RunModel() As Boolean
If CancelExectuion Then Return CancelCleanup()
Do While True
SyncLock _sync
If _ConcurrentRuns < _MaxConcurrentRuns Then
Interlocked.Increment(_ConcurrentRuns)
Exit Do
End If
End SyncLock
Threading.Thread.Sleep(50)
Loop
'This is what will launch an individual process and close it when finished
ret = RunApplication(arg)
' The process has been closed so we decrement the concurrent runs
Interlocked.Decrement(_ConcurrentRuns)
Return ret
End Function
The goal is to let only one thread exit the while loop at a time, I'm not able to catch it in the debug mode however in the task manager it will occasionally go 1-3 processes over what it's supposed to use. This makes me assume that somehow multiple threads are getting inside the synclock somehow, but I have no clue how that could be happening.
I will be very grateful for any and all help that can be provided, thanks for taking the time to read my question.
So it appears that my solution works for this, I don't want to delete this question because it might be helpful to somebody else in the future.
Answer: Use better process monitoring software / set priority to high in task manager.
I am currently making a vb program that i plan to make very big. I have a decent knowledge of visual basic but today i came across something i do not understand. Because of the huge size of my program , i decided to try and keep the program as organized as possible by putting specific subs in modules. These subs consist of httprequest , webbrowsers(control), webclients and alot of loops. In order to prevent these subs from lagging my main application i thread them using threading.thread and i start them from my main form. But this leads to two problems.
Problem 1: The threads cannot in any way interact with the main form.
Once the a httprequest or webclient collects the information from my desired website, i am trying to make it add the info to a listbox in my main form, So what i did is it typed
Msgbox("Info Sent")
form1.listbox1.items.add(String)
The first messagebox will show but although the code right under it runs, nothing is added to the first forms listbox.I am not using delegates to transfer the information, instead, although its not a good habit, i am using checkforillegalcrossovers.
Problem 2: Threading with a webbrowser.
Threading with a webbrowser using threading.thread also does not work because it causes an active x error. After looking it up i found that a solution was to use a single threaded apartment but this would not work because i may need multiple threads running off the same sub at once.
One solution that i have found to this problem is creating another form completely and setting it invisible, and since the form is its own thread i do not need to use threading.thread , but the problem comes when i am trying to create multiple threads, or else i can somehow dynamically create the threads and put the subs inside of it programically this method wont work And even if it does i feel that it is sloppy so i will leave this for one of two last resorts.
The other solution is the most simple one in which i just put all of the code in the main form, but if i keep on doing that form1 is gonna become huge and sloppy, doing this wont solve the webbrowser problem either and even when using regions i still feel that something that 1000+ lines deserves its own class.
There must be some solution out there that solves these problems. Any help would be appreciated, Thanks.
I checked my code for updating the progress bar, and using a single thread with synclock will NOT work. They way I make it work is perform the step of the pbar each time after a thread is started as I have limited total threads (say less than 5 threads). Thus, even the progress bar steps before the threads are finished, but it will not progress further before new threads started. It is not 100% accurate but it more or less telling the progress
'update the progress bar
some_form.PBar1.PerformStep()
' This while loop is to count the existing running thread,
' and determine whether new thread should start
While 1
Dim t2 = New System.Threading.Thread(Sub() WaitForPermission())
t2.Start()
t2.Join()
If proceed_gen Then
Exit While
End If
End While
'Start doing what I need to do
Dim t1 = SomeSub()
t1.Start()
'End of code, as VB doest not have thread.detach()
Correct me if I am wrong, but you probably have to use a background worker. I know this is annoying, but this is the limitation of VB.net.
Or, you can have something like this (pseudo code, not tested)
structure some_struct
'define the strings you want to update, and their status such that
'main() knows if you need to update the stuff to the form
' You can also put how many threads are running, and the status of each thread,
'such that the main knows if all threads are completed
end structure
sub your_sub()
'Manipulate the website, and update the data structure with
'proper stuff you need
end sub
sub main(){
dim t1 = New System.Threading.Thread(Sub() your_sub())
t1.start()
' I am listing only one threads here, but start as many as you want
'check if there are strings that you need to update to the form
while 1
'check if there are any stuff you want to update from the data structure.
' Make sure you use synclock on the data structure, so each thread won't fight each other on accessing the data struct
dim should_update as boolean = false
should_update = 'Something thatyou should implement to judge whether you should update the form.
'You can start a thread and join it so the thread won't fight with other threads for accessing the data structure
dim some_string as string
if should_update
some_string = 'You may also need a thread to join to get the stuff you need. Dim the string as an array if it is required.
'You can also try pass by ref
'if you need to use thread to access the data structure to know if you need to update the form
form1.listbox1.items.add(some_string )
end if
end while
end sub
This is an ugly solution, but it will help you do the job...
I've read a lot of different questions on SO about multithreaded applications and how to split work up between them, but none really seem to fit what I need for this. Here's how my program currently basically works:
Module Module1
'string X declared out here
Sub Main()
'Start given number of threads of Main2()
End Sub
Sub Main2()
'Loops forever
'Call X = nextvalue(X), display info as needed
End Sub
Function nextvalue(byval Y as string)
'Determines the next Y in the sequence
End Function
End Module
This is only a rough outline of what actually happens in my code by the way.
My problem being that if multiple threads start running Main2(), they're dealing with the same X value as in the other threads. The loop inside of main2 executes multiple times per millisecond, so I can't just stagger the loops. There is often duplication of work done.
How can I properly divide up the work so that the two threads running simultaneously never have the same work to run?
You should synchronize the generation and storage of X so that the composite operation appears atomic to all threads.
Module Module1
Private X As String
Private LockObj As Object = New Object()
Private Sub Main2()
Do While True
' This will be used to store a snapshot of X that can be used safely by the current thread.
Dim copy As String
' Generate and store the next value atomically.
SyncLock LockObj
X = nextValue(X)
copy = X
End SyncLock
' Now you can perform operations against the local copy.
' Do not access X outside of the lock above.
Console.WriteLine(copy)
Loop
End Sub
End Module
A thread manager is required to manage the threads and the work that they do. Say it is desirable to split up the work into 10 threads.
Start the manager
Manager creates 10 threads
Assign work to the manager (queue up the work, let's say it queues up 10000 work items)
Manager assigns a work item to complete for each of the 10 threads.
As threads finish thier work, they report back to the manager that they are done and recieve another work item. The queue of work should be thread safe so that items can be enqueued and dequeued. The manager handles the management of work items. The threads just execute the work.
Once this is in place, work items should never be duplicated amongst threads.
Use a lock so that only one thread can access X at a time. Once one thread is done with it, another thread is able to use it. This will prevent two threads from calling nextvalue(x) with the same value.
I'm having some timing problems in a unit test of some of my vb code.
I set up a test harness by checking for and then deleting records added to the db in the previous testing session, and then I test my recording adding code by adding back the same records.
Interestingly this code works fine when there is a break in the debugger, but fails with a "duplicate key" exception when I let it run with no breaks, which leads me to believe there is some kind of concurrency issue.
The basic metacode is as follows:
DoTest()
dim j as datacontext
dim recs = from myrecs in j.mythings select myrecs where myrecs.key="key1" or
myrecs.key = "key2"
if recs.count > 0
for each rec in myrecs
j.mythings.deleteonsubmit(rec)
next
j.submitchanges()
end if
j.dispose
dim tc as new tablecontroller()
tc.addrecordtomytable("key1","value1")
tc.addrecordtomytable("key2","value2")
end
Class tablecontroller
Sub addrecordstomytable(key as string, value as string)
dim j as new mydatacontext
dim thing as new mything
thing.key = key
thing.value = value
j.mythings.addonsubmit(thing)
j.submitchanges
j.dispose
end sub
end class
I've confirmed that I'm properly deleted the previous added records, and this works fine as does adding the new records when I have a break in the code before I hit the add records step. but without the break, it throws duplicate key exceptions in the "addrecordestomytable" method suggesting that it hasn't grabbed the current version of the table when it creates the new data context in addrecordstomytable, even though the records should have already been deleted.
I've tried refreshing the table, but this doesn't seem to work either.
Note backing database is ms sql server 10
Suggestions?
This is not so much an answer as a trouble-shooting technique. Have you tried using the log property? i.e.
j.log = Console.Out
So that you can see the actual SQL generated to make sure it is what you expect? Other than that is there anything relevant in your test setup or tear down? Is there anything managing a transaction? Are there triggers running? In terms of the latter if there is a trigger that takes some time to run and then the delete is finalized that might explain what you're seeing. I guess LINQ syntax varies between VB and C#, which surprised me, because I don't think your comparison code as written is valid in C#, you would need ==, not =, for a comparison but since it works when you break in the debugger...
I have been creating multiple background threads to parse xml files and recreate new xml files. Now the problem I am having is that even though I use synclock on global variables, I will still at times get errors and I am sure that this is just the crude way of coding I am doing, but I was wondering if someone had a better option.
program flow =
access local folder and upload all files into list
strip each file into xml entries and put these entries into an arraylist
parse for specific values and enter these values into a database table
now create a thread and take the arraylist of entries and the thread will reparse
thread parses and creates a new xml file
main thread continues with another function and then goes and get a file from list
I will add some code to show problem areas but if I have declared global variable in use does the different threads overwrite that value in the variable causing contamination.
For Each g In resultsList
gXmlList.Add(g)
Next
Dim bgw As New BackgroundWorker
bgw.WorkerSupportsCancellation = True
AddHandler bgw.DoWork, New DoWorkEventHandler(AddressOf createXML)
AddHandler bgw.RunWorkerCompleted, AddressOf WorkComplete
threadlist.Add(bgw)
bgw.RunWorkerAsync()
Private Sub createXML()
num += 1
Dim file As String = Module1.infile
xmlfile = directoryPath & "\New" & dateTime.Now.ToUniversalTime.ToString("yyyyMMddhhmmss") & endExtension
Thread.Sleep(2000)
Dim doc As XmlDocument = New XmlDocument
**xwriter = New XmlTextWriter(xmlfile, Encoding.UTF8)** this is where ioexception error
xwriter.Formatting = Formatting.Indented
xwriter.Indentation = 2
xwriter.WriteStartDocument(True)
xwriter.WriteStartElement("Posts")
I have global variables through out the app and should I be locking each one and does this not make using threads then useless.
Dim j As Integer = 0
I believe your biggest problem is not knowing what features in .Net are thread safe. A list for example is not (a dictionary is). While you may get away with it you will eventually run into problems with locking, etc.
Your using classes and variables that are not thread safe. Any time you are working with threads you have to be Extremely careful with locking. To answer your question, yes, you have to lock and unlock everything you are working with unless the type / method specifically handles it for you.
There are a lot of multi threading (PLINQ for example) in .Net 4.0 which handle a lot of the "grunt work" for you. While you should learn and understand how to do thread safe code yourself it will give you a head start.
Try passing the data into the createXML() method. That may help isolate the code from other data being accessed. I would suggest reading up on threading and learning how to do it without a background worker.
Global variables are generally a bad idea. Given your VB code I'm guessing this is a carry over from the VB6 world for you. That's not in any way intended to be insulting, just trying to help advance your skills forward. Variable scope should be as confined as possible.
Another thought looking at your code is to learn how to use String.Format() when building strings / paths.
Simple manual thread in VB to get you started:
Dim bThread As New Threading.Thread(AddressOf createXML)
bThread.IsBackground = True
bThread.Start()
Well if you are having issues with thread locking then you can simply wrap your action in the following manor.
'This will need to be out of scope so that all threads have access to it
Dim readerWriterLock As New Threading.ReaderWriterLockSlim
readerWriterLock.EnterWriteLock()
xwriter = New XmlTextWriter(xmlfile, Encoding.UTF8)
'other logic
readerWriterLock.ExitWriteLock()
'anything reading from this would need to have the following
readerWriterLock.EnterReadLock()
'logic
readerWriterLock.ExitReadLock()
Try this and then if not successful post the exception message and any other information that you can.